1 // Copyright 2020 The Pigweed Authors 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); you may not 4 // use this file except in compliance with the License. You may obtain a copy of 5 // the License at 6 // 7 // https://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, WITHOUT 11 // WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the 12 // License for the specific language governing permissions and limitations under 13 // the License. 14 15 // Provides an implementation of the CRC-16-CCITT or CRC-CCITT checksum, which 16 // uses the polynomial 0x1021: 17 // 18 // x^16 + x^12 + x^5 + 1 19 // 20 // with initial value 0xFFFF. See https://www.zlib.net/crc_v3.txt. 21 #pragma once 22 23 #include <stddef.h> 24 #include <stdint.h> 25 26 #ifdef __cplusplus 27 extern "C" { 28 #endif // __cplusplus 29 30 // C API for calculating the CRC-16-CCITT of an array of data. 31 uint16_t pw_checksum_Crc16Ccitt(const void* data, 32 size_t size_bytes, 33 uint16_t initial_value); 34 35 #ifdef __cplusplus 36 } // extern "C" 37 38 #include <span> 39 40 #include "pw_bytes/span.h" 41 42 namespace pw::checksum { 43 44 // Calculates the CRC-16-CCITT for all data passed to Update. 45 class Crc16Ccitt { 46 public: 47 static constexpr uint16_t kInitialValue = 0xFFFF; 48 49 // Calculates the CRC-16-CCITT for the provided data and returns it as a 50 // uint16_t. To update a CRC in multiple calls, use an instance of the 51 // Crc16Ccitt class or pass the previous value as the initial_value argument. 52 static uint16_t Calculate(std::span<const std::byte> data, 53 uint16_t initial_value = kInitialValue) { 54 return pw_checksum_Crc16Ccitt( 55 data.data(), data.size_bytes(), initial_value); 56 } 57 58 static uint16_t Calculate(std::byte data, 59 uint16_t initial_value = kInitialValue) { 60 return Calculate(ConstByteSpan(&data, 1), initial_value); 61 } 62 Crc16Ccitt()63 constexpr Crc16Ccitt() : value_(kInitialValue) {} 64 Update(std::span<const std::byte> data)65 void Update(std::span<const std::byte> data) { 66 value_ = Calculate(data, value_); 67 } 68 Update(std::byte data)69 void Update(std::byte data) { Update(ByteSpan(&data, 1)); } 70 71 // Returns the value of the CRC-16-CCITT for all data passed to Update. value()72 uint16_t value() const { return value_; } 73 74 // Resets the CRC to the initial value. clear()75 void clear() { value_ = kInitialValue; } 76 77 private: 78 uint16_t value_; 79 }; 80 81 } // namespace pw::checksum 82 83 #endif // __cplusplus 84